如何从R中的这些电子邮件中提取用户名？例如：<Angelwgsx2@aol.com>到Angelwgsx2。
<Angelwgsx2@aol.com>, <Jason.Bass2@COMPAQ.com>, <alaska_turtles@yahoo.com>, <Vettel22@flash.net>, <Blondi46@aol.com>, <ccoffee@anpower.com>, <cassiecorcoran@hotmail.com>, <charityp@flash.net>, <moonriter1@aol.com>, <ckendal@comp.uark.edu>, <delena38@home.com>, <deniesed@hotmail.com>, <dndlitch@btigate.com>, <Eric.Bass>, <marstersco@earthlink.net>, <whmfgm@yahoo.com>, <starlit_gazer@yahoo.com>, <Ggstops@aol.com>, <greenup@airmail.net>, <jimmycheer@yahoo.com>, <hmcgill-satx@worldnet.att.net>, <janet.corcoran@verizon.com>, <strait_line@yahoo.com>, <wxranch@airmail.net>, <jayjayjarv@yahoo.com>, <jwheeler45@home.com>,